Welder

ABSTRACT

One of two small workpieces that are to be welded together is slidingly mounted in a fixed workholder and the other is firmly gripped by a movable workholder. To carry out an operating cycle, the movable workholder is reciprocated by two lobes of a cam that makes on revolution when momentarily connected to a relatively large mass that rotates at constant velocity. Initially the first slidable workpiece is placed at random at a position that is advanced slightly from the position desired for the welding operation but the first reciprocation of the second workpiece is against the slidable workpiece to retract it precisely to the desired position for a welding operation. In carrying out the second reciprocation, the two workpieces are charged by capacitance and as the gap between the two workpieces narrows a high frequency pulse triggers an arc between the two workpieces and the continued advance of the second workpiece crowds the two workpieces together for final fusion.

United States Patent Phillips et al.

[451 Dec. 26, 1972 [54] WELDER [72] Inventors: Delbert L. Phillips,Malibu; Lewis Clark Feightner, Chatsworth, both of Calif.

[73] Assignee: New Twist Connector Corporation,

2 Santa Monica, Calif.

[22] Filed: June 1, 1970 [21] Appl. No.: $4,056

Related u.s. Application on.

[62] Division of Ser. No. 715,773, March 25, 1968, Pat.

[52] [1.8. CI. ..2l9/97, 219/95, 219/161 [51] Int. Cl. ..B23k 9/00, B23k11/04 [58] Field of Search ..219/95, 96, 97, 98, 100,113, 219/161 [56]References Cited UNITED STATES PATENTS R17,949 2/1931 Chubb ..219/96 X3,254,194 5/1966 Phillips ..2l9/l 13 X 3,400,239 9/1968 Fahrenbach......219/97 3,505,494 4/1970 Ruetschi ..2l9/95 X FOREIGN PATENTS ORAPPLICATIONS 1,246,141 8/1967 Germany ..2l9/98 Primary Examiner-J. V.Truhe Assistant Examiner-Hugh D. Jaeger Attorney-Smyth, Roston & Pavitt[5 7] ABSTRACT makes on revolution when momentarily connected to arelatively large mass that rotates at constant velocity. Initially thefirst slidable workpiece is placed at random at a position that isadvanced slightly from the position desired for the welding operationbut the first reciprocation of the second workpiece is against theslidable workpiece to retract it precisely to the desired position for awelding operation. In carrying out the second reciprocation, the twoworkpieces are charged by capacitance and as the gap between the twoworkpieces narrows a high frequency pulse triggers an are between thetwo workpieces and the continued advance of the second workpiece crowdsthe two workpieces together for final fusion.

15 Claims, 12 Drawing Figures WELDER CROSS-REFERENCES TO RELATEDAPPLICATIONS This is a division of application Ser. No. 715,773, filedMar. 25, 1968, now US. Pat. No. 3,609,284.

BACKGROUND OF THE INVENTION The invention relates to an arc weldingtechnique of the character disclosed in the three Phillips U.S. Pat.Nos. 3,254,193, 3,254,194 and 3,254,195 and it is to be understood thatany of the circuits disclosed in the three prior patents may be adaptedfor use in the present disclosure even though the circuit disclosedherein is highly advantageous and has special utility.

All three of these patents teach that with an electrode spaced from aworkpiece or with two workpieces spaced from each other by a suitablegap, an arc may be created across the gap by first employing capacitormeans to create a potential across the gap and then employing a highfrequency pulse to trigger an arc.

The present invention is directed primarily to the problem of developinga means and a method of joining small workpieces by arc welding inhighly accurately repeated operating cycles wherein the requiredduration of the arc may be as low as one third of a millisecond andusually does not exceed eight milliseconds. The basic problem is toprovide exceedingly accurate and unvarying control on such a small timescale.

The Phillips U.S. Pat. No. 3,254,193 is of special interest in that itteaches mounting one of the two workpieces on a fixed workholder,mounting the other workpiece on a relatively light workholder and thenapplying force to the workholder to accelerate it to high velocity tobring the two workpieces together with the are triggered as the gapnarrows between the two workpieces. The movable workholder is normallyretracted by a suitable spring and is electromagnetically ad vanced byenergization of coil means to carry out an operating cycle. Thisprocedure is operative for its purpose but has certain disadvantageswhen the primary requirement is accurate adjustability and accuraterepetition of operating cycles and especially so when the duration ofthe arc must be controlled within microseconds and the operating cyclemust be repeated rapidly for high speed production.

The described prior art procedure has the following disadvantages:

1. Friction is a variable factor and the presence of a foreign particlemay change both the rate of movement of the workholder and .the timingof the arc relative thereto.

2. Since the advance of the workholder to carry out an operating cycleis increasingly opposed by the return spring, the spring is a variablefactor.

3. The electromagnetic driving force increases exponentially at one ratewhile the opposing resistance of the spring increases at a differentrate to make close adjustment difficult.

. Each operating cycle necessarily includes time for acceleration of theworkholder as a free body prior to the actual welding operation and forreasons including the above factors the rate and degree of accelerationof the free body is not subject to the degree of control required foraccurate repetition of an operating cycle.

5. The triggering of the arc is responsive to changes that occur in thecurrent flow in the circuitry that includes the coil for actuating theworkholder and largely because of the heretofore stated factors thetiming of the triggering of the arc may vary from cycle to cyclerelative to the position of the moving iron core.

6. The extent to which the two workpieces are crowded together for finalfusion depends on a number of factors including: the mass of theworkholder; the velocity of the workholder at the moment of impactbetween the two workpieces; theeffect of the spring in decelerating theworkholder; and the resistance to deformation of the heated portions ofthe twoworkpieces. Obviously adjusting the crowding action to the needsof different workpieces is complicated.

7. Since the moving workpiece is part of the electromagnetically drivenworkholder, changing over from one size of workpiece to anotherintroduces a variable in that it changes the mass that iselectromagnetically accelerated.

8. It has been found that an arc welding device of the character musthave a certain relatively wide range of flexibility. At one extreme theare employed to join two pieces of copper must be intense for generatingheat at a relatively high rate but must be of short duration because ofthe high conductivity of copper. At the other extreme, the welding of analloy containing zinc is made possible for the first time by employing alow intensity are of prolonged duration. Thus for welding copper the arcmay have a duration of A: of a millisecond while an arc for a zinc alloymay have a duration of 8 milliseconds. In addition the rate at which thegap is closed between two workpieces must be variable because thedifferent physical properties of different molten metals affects theirbehavior as they are forced together. This prior art apparatus isinherently incapable of flexibility in these important respects.

The present invention is not only directed to the elimination of thesedisadvantages but also is directed to important improvements in thecircuitry for producing the arc.

SUMMARY OF THE INVENTION In a preferred embodiment of the invention fora fully automatic operating cycle, a rotary cam means formed with twocircumferentially spaced lobes is engageable with a continuouslyrotating structure of relatively high mass through speed-reducinggearing by means of a clutch which rotates the cam for one fullrevolution for one complete cycle of operation and then the cam isstopped at its starting position by a suitable brake. A first workpieceis frictionally slidingly mounted in a stationary workholder and thesecond workpiece is firmly mounted in a movable workholder that isreciprocated twice by a follower cooperating with the two lobes of thecam means. The first slidable workpiece is located in a random manner onthe first workholder at a position advanced somewhat towards the secondworkpiece and when the second workpiece is reciprocated by the first camlobe, the second workpiece encounters the first workpiece and retractsthe first workpiece accurately to a starting position for carrying outthe work cycle. When the second workholder retracts, the distancebetween the two workpieces is precisely the magnitude of its retractionregardless of the initial position of the first workpiece in the firstworkholder and regardless of the initial position of the secondworkpiece in the second movable workholder. Thus the first reciprocationresults in accurate predetermined starting gap between the twoworkpieces.

After a short pause controlled by a lower dwell on the rotary cam means,the movable workholder is reciprocated again to close the gap betweenthe two workpieces and at a precisely predetermined point in therotation of the cam means an arc is triggered between the two spacedworkpieces to melt the metal of the confronting surfaces of the twoworkpieces and the second workholder continues to advance the secondworkpiece after the two workpieces abut each other, the additionaladvance crowding the workpieces together for complete fusion of theheated portions of the workpieces. The force with which the fusingworkpieces are crowded together may be limited to any desired magnitudeby simply varying the friction with which the workpiece is slidinglyretained in the stationary workholder.

At the start of the operating cycle, the two workpieces are simplyplaced at suitable positions on the two workholders and as soon as theoperating cycle is started the two workholders automatically grip thetwo workpieces. At the end of the operating cycle the two workholdersautomatically release the welded product and then the welded product isautomatically ejected.

After the first reciprocation of the movable workholder, a voltage isplaced across the two workpieces and subsequently the arc is triggeredin response to arrival of the second workpiece at a preciselypredetermined point in its second movement towards the first workpiece.To create the desired voltage across the two workpieces, the cam meansoperates a relay for connecting capacitor means to a voltage source andalternately to connect the capacitor means to the two workpieces; meanscontrolled by the cam means keeps the initially engaged clutch engageduntil a suitable point near the end of the operating cycle; furthermeans controlled by the cam means operates solenoids for gripping thetwo workpieces; further means operated by the cam means controls a thirdsolenoid for ejecting the finished product; and still further allimportant means controlled by the cam means triggers the are at anexactly predetermined point in the approach of the movable workpiece tothe stationary workpiece.

The manner in which the described cyclic mechanism avoids the'previouslymentioned disadvantages of the prior art mechanism isexplained as follows:

1. With a driving structure of relatively large mass rotating at aconstant velocity for a normal steady state condition, frictionalresistance to movement of the driving mass is eliminated and with themass of the driving structure far exceeding the mass of the movableworkholder, frictional resistance to movement of the workholder may beneglected.

2. A spring is provided to hold the workholder follower against the cammeans and to return the movable workholder after each advance but thespring force is more than adequate to maintain constant contact betweenthe workholder follower and the cam means with the result that thespring itself does not affect the operating cycle and especially sobecause of the mass of the driving structure.

3. Since the cam means is fully accelerated by the high momentum of thedrawing mass prior to actuation of the movable workholder thedisplacement of the workholder follower by the leading slope of thesecond cam lobe is at an accurately predetermined rate for accuratecontrol of the rate at which the gap between the two workpieces isclosed after the arc is triggered.

. Since no time interval is required in the operating cycle foracceleration of the constantly rotating mass, acceleration is removed asa factor and the operating cycle may be correspondingly shortened.

. Since the arc is triggered in response to the arrival of theworkholder follower at a precisely predetermined point in the rotationof the cam means, the timing of the triggering of the arc is preciselypredetermined in advance of mutual abutment of the two heatedworkpieces. Thus the correlation of the ignition of the arc with theclosing of the gap may be accurately maintained over a long productionrun.

. Since the first reciprocationof the movable workholder accuratelyestablishes a predetermined gap between the two workpieces and since theadvance of the second workpiece on the second reciprocation of themovable workholder exceeds the first advance by a predeterminedincrement, the extent to which the two workpieces are crowded togetherin the final fusing step is accurately predetermined and is constantover a large production run. With the crowding action accomplished bythe cooperation of the follower and the cam means, the crowding actionis not determined directly by the magnitude of the moving mass nor is itaffected by any spring means nor is it necessarily limited by theresistance to deformation of particular workpieces.

. Changing over from the processing of workpieces of a given mass to theprocessing of workpieces of a different mass only slightly affects therate at which the two workpieces are brought into mutual contact becausethe ratio between the high momentum of the driving mass and therelatively small mass of the movable workpiece is exceedingly high, say220021. This fact may be appreciated when it is considered that inthepreviously described cycle of operation disclosed in the Phillips US.Pat. No. 3,254,193 the ratio between the approximately one ounce weightof the workholder and the one-tenth gram weight of a typical smallworkpiece mounted on the core is approximately 260:1 whereas in thepresent invention the ratio between the weight of the driving structureand the weight of the same workpiece is approximately 10,000: 1. It maybe readily appreciated that with this overpowering ratio, the drivingmass acts like a stabilizing flywheel to insure that all of theoperating cycles are precisely identical. Changing over to a differentworkpiece of a different weight may vary the operating cycle but only toslight degree and in any event the new cycle pattern is accuratelyreproduced on each cycle.

Since the momentum of the driving structure on which the operating cycleis based varies with its velocity; it is desirable to move the drivingmass at high velocity. On the other hand, high velocity of the drivingmass may result in moving the two workpieces together at an undesirablyhigh velocity. A feature of the invention in this regard is theprovision of suitable speed reducing means for operatively connectingthe movable workpiece with the driving mass. In the initial practice ofthe invention the motor for driving the cam means rotates at a desirablehigh velocity for the sake of high momentum but reduction gearingreduces the angular velocity of the cam means to one-sixth of theangular velocity of the motor rotor and, if desired, further reductionin the velocity imparted to the movable workpiece may be provided byforming the lobes of the cam means with gradual leading slopes.

As will be apparent, the new circuitry has unique advantages includingadjustability of the intensity and duration of the are, suchadjustability being provided by adjustability in the capacity of thecapacitor means that is charged to provide the energy of the arc, aswell as adjustability in the voltage of the applied charge andadjustability in the impedance of the arc-sustaining circuit. In thepreferred practice of the invention a choke coil may be placed in thearc-sustaining circuit whenever desired and different taps on the chokecoil may be used for different degrees of impedance by the choke coil.

The flexibility of the operating cycle may be appreciated when it isconsidered that the magnitude of energy expended in the arc may bevaried at will and the duration of the arc may be varied independentlyof the total are energy. A further feature of the invention in thisregard is that the timing of the triggering of the are relative to themoment of contact of the two workpieces is also readily adjustable bythe simple expedient of changing the position of a contact thatcooperates with the cam means to trigger the arc. In the preferredpractice of the invention the triggering contact is moved by a manuallyoperable knob that shifts the contact by screw action and a pointeroperated by the knob traverses a scale that is calibrated inmicroseconds of duration of the arc.

With exact control over the three factors of arc energy, arc durationand the timing of the triggering of the arc relative to the closing ofthe gap between the two workpieces, the welding function may be readilyadjusted to meet the specific requirements of any particular pair ofworkpieces. Thus the energy of the arc may be adjusted as required formelting different metals and for melting different quantities of thedifferent metals and the duration of the arc may be shortened tominimize the melted zones of the workpieces or may be extended whendesirable to vaporize oxides and impurities prior to the moment ofmutual abutment of the workpieces.

The various features and advantages of the invention may be understoodfrom the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to beregarded as merely illustrative:

FIG. 1 shows somewhat schematically and partially in a perspective view,the mechanical part of the welding apparatus in accordance with thepresent invention;

FIG. 2 illustrates a cross-sectional view through the guide system forone of the workpiece holders used in the equipment shown in FIG. 1.;

FIG. 3 is a development of the cam used for controlling the motion ofone of the workpiece holders shown in FIG. 1;

FIG. 4 illustrates somewhat schematically a circuit diagram, partiallyas a block diagram, of the control of the welding current and areignition control circuit in accordance with a first embodiment of thepresent invention;

FIG. 5 illustrates an alternative embodiment of this invention partiallyas block diagram and partially as circuit diagram;

FIG. 6 is a diagram showing developments of five cams on a common camshaft that may be employed to carry out the operating cycle;

FIG. 7 is a schematic view showing different stages in the tworeciprocations of the movable workholders;

FIG. 8 is a simplified elevational view of the two workholders;

FIG. 9 is a side elevational view of the stationary workholder;

FIG. 10 is a fragmentary view partly in side elevation and partly insection showing the mechanism for varying the timing of the triggeringof the are relative to the closing of the gap between the twoworkpieces;

FIG. 11 is an elevational view as seen along the line 11 11 of FIG. 10showing a scale that is associated with the mechanism in FIG. 10, thescale being calibrated in microseconds of duration of the arc; and

FIG. 12 is a wiring diagram modification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Proceeding now to the detaileddescription of the drawings, FIG. 1 thereof illustrates a weldingapparatus in accordance with the present invention. The illustration issomewhat schematically but partially in a perspective view. Of specificinterest is the welding of small elements. For example, in FIG. 1,numerals 10 and 11 denote two workpieces to be welded together. Element10 is a semiconductor device such as a transistor, an integratedcircuit, etc., encapsuled in a metallic shell. The other workpiece is aconnecting wire 11 to be connected to element 10. One can see that thewelding process is a most critical one because an excessive heatdevelopment will destroy the semiconductor device in the interior of thecontainer, whereas too little thermal energy developed will produce anunsatisfactory weld. Since effective thermal energy is determined by thebalance of heat inflow and outflow at any instant, the duration of theperiod during which a particular amount of electrical energy is suppliedand converted into thermal energy is most critical. Therefore, thewelding, i.e., thermal, energy and the development of that energy, i.e.,the duration of the weld, all have to be determined rather accurately inorder to produce a satisfactory weld which does not destroy the product.

The welding device proper includes a workholder 20 having an opening orpocket 21 into which a workpiece can be inserted. The pocket 21 has aconfiguration adapted to receive and position a particular workpiece inthe form of an encapsulated transistor. Of course,a different type ofholder may be used for a workpiece of different configuration. It isimportant that the particular holder positions the one workpiece in amanner to expose a surface portion thereof to which the other workpieceis to be welded.

Reference numeral 22 denotes another workholder which is stationary.Holder 22 has a groove 23 over which is placed a clamp 24 forfrictionally holding a workpiece in the form of a wire 11 in the groove.The clamping action is strong enough to grip the workpiece effectivelyto carry out the fusing or forging of the two workpieces but is lightenough to permit initial slippage for the purpose of accuratelydetermining the gap between the two workpieces.

The workholders are at least partly made of metal so that electricvoltage potentials can be applied to the workpieces thereon. It followsthat workholders 22 and 24 must be electrically insulated from eachother. A wire 25 connects the workholder 22 to a welder current controlcircuit 100, to be described more fully below, and a flexible electricalconnection 26 leads from the welder control circuit 100 to theworkholder 20.

The workholder 20 is movably disposed on a vertically movable rod 30.The rod 30 is prevented from tilting by a guiding arrangement 31. Aportion of the guiding arrangement is shown in a cross-sectional view inFIG. 2. The rod 30 may have a portion hexagonal cross section that isguided by two sets of three rollers each; one of the sets is shown inFIG. 2. There are two rollers 32 and 33 which have a fixed axis ofrotation and engage two different sides of the rod 30. The axes of therollers 32 and 33 are at an angle of 120. The shaft of the third roller34 is under the influence of springs 35 urging the shaft towards the rod30. The springs thus provide for positive engagement of all threerollers with the rod. As stated above, there is a second set of rollersfor additionally guiding the rod 30. If the second set of guide rollersis accurately mounted in vertical alignmerit with the one illustrated,rod 30 is accurately guided for vertical longitudinal motion.

The lower end of the rod 30 terminates in a cam follower 36. A spring 37is anchored at one end to a stationary part of the device and its otherend is anchored to a pin 38 which, in turn, projects from rod 30. Thespring is biased to urge pin 38 in down direction to thereby urge thefollower 36 of the rod 30 into engagement with a cam 40. The cam iscapable of pushing bar 30 in up direction, while spring 37 retracts bar30 when the moving contour of cam 40 so permits.

The cam 40, and particularly the periphery 41 thereof, servesadditionally to control a switch 51 which has an appropriate followerarm and which is connected electrically to the welder control circuit100 in a manner to be described more fully below. A projection 48 on thecam 40 serves to control a second switch 52 which likewise pertains tothe welder control circuit 100 and to which will be made reference morefully below. On this particular embodiment of the invention the switch51 responds to the same cam lobes that control the follower 36 of theworkholder rod 30.

Cam 40. is provided with a spur gear 42 meshing a pinion 43 on a shaft44 whichjis operatively connected to a brake-clutch assembly, generallydesignated 45, comprising a brake 45a and a clutch 45b. The rotary inputof the clutch 45b is derived from a shaft 46 driven by a synchronousmotor 47. The synchronous motor 47 is continuously connected, at leastduring extension welding operations, to an a-c source of standardfrequency.- Motor 47 thus imparts to the shaft 46 a preciselypredetermined rate of rotation. The brakeclutch assembly 45 iscontrolled by a common switch 50, the brake 45a disengaging and theclutch 45b engaging in response to' closing of the switch and viceversa. As will become apparent more fully below, switch 50 initiates acycle of operation that is carried out b one revolution of cam 40.

A welding operation, in summary, is carried out in the following manner.While the motor 47 runs continuously, the encapsuled transistor element10 is placed in the cavity or pocket 21 of the workholder 20 and thewire 11 is placed in the groove 23. The position of capsule 10 isdefined by the contour of pocket 21, but wire 11 is variablypositionable in groove 23 of holder 22. Subsequently switch 50 is closedso that clutch 45b energized. The energized clutch couples cam 40 tomotor 47. The cam 40 then performs one revolution. After a completerevolution either the switch 50 is opened manually or through aconventional control circuit which may include an additional cam, or cam40 itself may-be used to interrupt the clutch circuit. This type ofinterrupt control is well known and of course, the control may becarried out manually if desired.

During the one revolution the cam 40 controls the entire weldingoperation. As will be described more fully below, the cam causes the arm30 first to preposition the two elements 10 and l l to define the sizeof the gap across which an arc is to be struck. Thereafter the switches51 and 52 are closed sequentially to energize the welder control circuitin that a low voltage is applied first to the wires 25 and 26 and to theworkpieces and subsequently a high voltage is developed to strike anarc. In precise synchronism with are ignition the cam 40 moves the twoworkpieces 10 and 11 again towards each other, brings them into contact,maintains that contact until colled and retracts them together.

Proceeding now to the description of FIG. 3 there is shown thedevelopment of the contour of periphery 41 of cam 40. The base line t inFIG. 1 corresponds to the smallest radius of the cam 40 with referenceto its axis of rotation and it defines, therefore, the lowest portion ofthe cam (except for a modification to be discussed separately). The camprovides for reciprocating motion of follower 36, for example, in thevertical direction.

' Hence, cam radius r defines the lowest position of follower 36 (and,of course, of workpiece holder 20). The follower is at this lowestposition when the system is at rest, i.e., in between welds. The contourof the leftmost side of the diagram shown in FIG. 3 has this radius rand defines the position of follower 36 at the beginning of theoperating cycle. It is convenient to describe the various portions ofthe cam contour with reference to the sequential control effects exertedby them upon workholder 20 as these portions progressively control theposition of the'follower 36 during rotation of the cam 40.

In FIG. 3 the particular cam portion controlling the idle position offollower 36 which actually is an indentation in the cam, is .furtheridentified by t which means that we assume that at the starting time tthe switch 50 may be closed to initiate rotation of the cam. The portion411 of cam 40 that subsequently controls follower .36 is characterizedby an increasing radius thus causing the follower 36 along withworkholder 20 to move in upward direction. The cam portion 411terminates in the lobe 412 which actually is a portion of constantradius r of the cam disk 40, the radius r, being larger than the radiusr,,. Therefore, when the follower 36 reaches the portion 412 it has beenmoved in upward direction by the difference r r It was stated above theworkpieces and 11 were placed into the respective workholders and 22prior to the time t when the workpiece holder 20 is at its lowermostposition. Also, it was stated that wire 11 does not have to bepositioned very accurately into groove 23, but the lower tip of wire 11must be initially spaced from the other workpiece 10 at a distance whichis smaller than r r In fact the two workpieces may be initiallypositioned in contact with each other provided that workpiece 11 is nothigher than r r above workpiece 10.

It follows, therefore, that during the time the cam portion 411 ofincreasing radius advances the position of follower 36, workpiece 10will meet the wire 11 but thereafter workpiece 10 in workholder 20continues to move upwards. As was stated above, the clamping force forthe wire 1 1 is slight and as the upward stroke of the workholder 20continues, the workpiece l0 pushes the wire 11 also in up direction.

At time t, the upward motion of follower 36 stops because the camportion 412 succeeding portion 411 is a dwell of the radius r Thus,after time t workholder 20 and workpieces 10 and 11 are temporarily atrest. It is apparent that it is immaterial which workpiece is I shiftedrelative to its holder and which one stays fixed, or whether both ofthem shift. The initial position of the two workpieces is completed bytime t,. Presently the workholder 20, acting through the workpiece 10,has now actually placed the wire 1 1 in a particular position relativeto its holder 22. If, subsequently, the workholders are moved apart by aparticular distance, the workpieces will be automatically spaced apartby that distance.

The dwell or plateau 412 of constant radius r does not have to be toolong but some length is required to provide for some settling so thatthe position of the wire 11 is positively defined. lt is emphasized thatup to that point no current flows through the welding system. At a time1 a gap between the two workpieces is initiated because a portion 413 ofcam 40 reaches the follower 36 which portion 413 is defined by adecreasing cam radius. Therefore, the spring 37 causes retraction of thefeeler arm 36, and the workholder 20, retracts accordingly. Thusworkpiece 10 separates from the workpiece 11 at the time 1 and continuesto retract therefrom. At the time I the cam portion 413 levels off to alower dwell 414 of constant radius r,,, and while follower 36 slidesover this lower dwell, workholder 20 is maintained at a particular,retracted position. The workholders have thus been retracted over adistance r r, as defined by the difference between the cam radii r r...The difference r defines also the present distance between the twoworkpieces, this distance being the maximum air gap distance over whichan arc may be ignited.

During the period in which the follower 36 maintains workholder 20 inretracted position, switch 51 is closed which may be at any time after 2for example at time 1 In response thereto the welder control circuit 100causes a low voltage to be applied to the wires 25, 26. As stated, thisvoltage is insufficient to strike an arc across the gap between the twoworkpieces 10 and 11, which gap is of the dimension r r Switch5 l ispositioned in advance of follower 36 with reference to the direction ofrotation of cam 40, and is operated by the lobe 416 of largest radius.The function of that lobe with reference to follower 36 will bedescribed below.

The switch 52 may be closed to trigger the are at any selected time tafter time t, and before the follower.36 climbs the cam slope 415 attime t at the level of the initial upper dwell 412 that is indicated bythe broken line 412a and thereby brings the heated workpieces together.The arc is extinguished when the follower 36 brings the two workpiecestogether, but because the cam slope 415 continues to rise above thelevel 412a, the two workpieces are forcibly crowded together to fusetheir molten end portions together. The second upper dwell 416 ofconstant cam radius r,, is reached at time t,. The welding arc currentflows during the period between the times and 2 The friction with whichthe wire 11 is held in holder 22 is sufficient to resist the initialcrowding force and only after the softened portions of wire 11 andelement 10 have been driven into each other does the wire 11 move bodilyin response to the crowding force.

In the time interval between t, and t the upper dwell 416 of constantradius r keeps the follower 36 stationary.

It will be recalled that switch 51 is angularly displaced from follower36 so that cam lobe 416 operates the switch earlier in a welding cyclethan the arrival of the follower 36 at this cam lobe. The switch 51 maybe closed by came lobe 416 at any time between t, and time At time t aportion 417 of declining radius of the cam reaches the follower 36 andspring 37 causes the workholder 20 to retract according to the slope ofcam portion 417. During the downward retraction of workpiece 10, wire 11is welded thereto and slips out from under the clamp 24.

At about the time 1 the operating cycle is completed and switch 50 opensto stop cam 40. The two pieces which have been welded together may thenbe removed from the workholder 20 in preparation for a new operatingcycle. i

It shall now be described how the switches 51 and 52 control the entirewelding process, to the extent that they are themselves controlled bycam 40. A representative example of the control circuit is shown in FIG.4.

Reference numeral 60 generally denotes an electric power supply unit forthe welding control circuit in accordance with the present'invention.The power supply includes a transformer 61 having a primary 62 which isconnected to the same external power supply source, for example, themains, as are motor 47 and brakeclutch assembly 45. This transformer 61has a core on which there are two secondary windings which are not shownin detail.

Reference numeral 63 denotes a low voltage d-c power supply for thewelder circuit which is also not shown in detail but it includes one ofthe secondary windings of transformer 61 for voltage step-down. The lowvoltage d-c source 63 includes further a conventional rectifier tosupply a particular d-c voltage potential to an output line 64, theoutput being variable in a rangeof 40 to 100 volts. The network 63 mayinclude additionally a voltage regulator such as, for example, atransistor serving also as rectifier and having in its control circuitsuitable, adjustable impedance means'for adjusting of the d-c voltagefor line 64. Alternatively or additionally the secondary winding oftransformer 61 feeding the a-c voltage to the rectifier in unit 63 maybe adjustable. All of these elements are conventional and do not requireelaboration, since they are shown in the above mentioned U.S. Pat. Nos.3,254,l93; 3,254,194; and 3,254,195. A second d-c output line 64bprovide d-c voltage at a different level.

Reference numeral 65 denotes a high voltage d-c power supply unit whichdoes not require regulation as the voltage constancy and the levelaccuracy of the mains suffices here. The unit 65 includes anothersecondary winding of the transformer 61, preferably having a highernumber of turns than the primary 62 to provide for voltage step-up. Theoutput line 66 of unit 65 receives a high d-c voltage, for example, of800 volts positive relative to ground, whereas a second output line 67of unit 65 receives a negative d-c voltage potential of 800 voltsnegative relative to ground, so that the potential difference betweenthe lines 66 and 67 is 1600 volts. These voltages will be used to feedan arc ignition circuit.

The d-c voltage of line 64 is passed to an adjustable capacitor bank 70.The capacitor bank includes a plurality of capacitors individuallyconnectible through resistors between the line 64 and ground so that aparticular amount of electric energy can be stored. The total chargedepends, of course, on number and size of the capacitors placed intocircuit to be charged and on the voltage applied through line 64 forcharging. Both total effective capacitance and voltage determine theamount of energy available for discharge. The electrical energyaccumulated in capacitor bank 70 can be discharged through the line 71,and the voltage in line 71 will be essentially the same as in line 64.

The lines 64 and'71 are now in addition governed by the contacts 76, 77of a-relay 75. The energizing coil of the relay 75 is under control ofthe switch 51, mentioned above. Switch 51 when closed connects relaycoil 75, between ground and line 64b which is a constant, non-adjustablelow-voltage d-c output of the unit 63. As long as relay 75 is notenergized contact 76 is closed and contact 77 is open. This is thenormal state as switch 51 is, in fact, normally open (up to time 1 aswas explained above). Therefore, the relay 75 is normally unenergized soas to permit the capacitor bank 70 to be charged through the normallyclosed contact 76. On the other hand, contact 77 is normally open toprevent any discharge of the capacitor bank 70, accidentally orotherwise, during the charging process. Moreover, contact 77 governs allthose circuit portions with which personnel may come into contact priorto the actual welding operation and the open contact 77 permits theprepositioning of workpieces as explained above.

When relay energizes, contact 76 opens and contact 77 closes to therebyprovide a connection'from the capacitor bank to a series circuit networkwhich includes directly a feed-through capacitor 78, a secondary winding82 of a saturable core type transformer 81, the line 25 mentioned aboveand one of the workpieces which, in this case, is the wire 11. As longas no are exists across the gap between workpieces l0 and 1 1, or aslong as the workpieces 10 and 11 do not contact each other, the highimpedance of the unionized gap holds that series circuit open even whencontact 77 is closed.

The wire 26 connects the other workpiece 10 to ground as was alreadymentioned above. Therefore, with a gap between the two workpieces l0 and11, the capacitor bank 70 can discharge when the contact 77 closes,provided there is an are between the two workpieces. As mentioned above,the switch 51 closes at time As shown in FIG. 1, the follower arm of theswitch 51 is positioned ahead of the follower 36 with respect to thedirection of the rotation of cam 40. Therefore, the lobe 416 which isthe one with the largest control radius r will enter the range of thefollower arm of switch 51 ahead of the follower 36. Particularly switch51 closes when follower 36 has completed the positioning of a workpiece10 at the desired gap distance from workpiece 11. Contact 77 is closedand the capacitor bank voltage becomes effective across the gap betweenthe workpieces l0 and 11 only after the prepositioning of the workpieceshas been completed, and when they are separated from each other by thecam lobe difference r r It is essential that the voltage then appliedacross the gap between the two workpieces be insufficient to strike anarc. Therefore, for igniting an are additional provision must be made aswill be described next.

The control circuit for arc ignition is divided into an arc ignitingcircuit, generally designated 80, and a trigger circuit, generallydesignated 90. The are igniting circuit 80 includes a multi-turnsecondary winding 82 of saturable core type transformer 81 that has aprimary winding 83 of but a few turns. For example, the winding 82 mayhave 29 turns and the winding 83 may have 2 V2 turns so that the voltagestep-up ratio is about 1:12 for developing an extremely high voltageacross the secondary winding 82.

One end of the primary 83 is connected through a capacitor 84 to anelongated, high refractory type electrode 85a of an electrode systemthat is generally designated 85. Representatively, electrode 85a may bea cylindrical rod of 1 V2 inches length and A inch diameter. The otherside of the winding 83 is connected through a second capacitor 87 to anelectrode 85b which is similar to electrode 85a and which is also in theelectrode system 85. Capacitor 87 is overbridged by a resistor 89 of,for example, 15 KO. Electrodes 85a and 85b are placed in parallel(physically) and at a distance of about /2 inch from each other. Theyarerespectively connected with-their other ends to the high voltage d-cpower supply lines 66 and 67 using individual high ohmic resistors 88aand 8812, respectively for the connection. Each of the resistors 88a and88b may have a resistivity of the order of 100 K O. A third electrode85c, in the electrode system 85 is of similar configuration as the othertwo electrodes and is interposed between them and in parallel spacialrelationship thereto.

Electrode 85c does not extend all the way into the gap betweenelectrodes 85a and 85b. Thus, there are now defined three air gaps. Thefirst one, 86a, is between electrodes 85a and 85b beyond electrode 850.The second gap 86b is between electrodes 85b and 85c, and the third gap86c is between electrodes 85c and 85a.

The capacitor 84 is connected directly to the high voltage power supplysource 65 through resistors 88a, 88b and 89. Thus, capacitor 84 isnormally charged to 1600 volts. The charge time is short in relation tosequential welding cycles as defined by revolutions of cam disk 40, sothat the capacitor 84 is always charged when needed. The gap 86a is sowide so that the 1600 volts thereacross are not sufficient to strike anarc. The electrode 850 is normally grounded so that across each of thegaps 86b and 86c there are 800 volts and these gaps are likewise toolarge for ignition of an arc. Thus, normally there is no arc across anyof the gaps in the electrode system 85, and there is no voltage acrossthe windings 82 and 83. Also, any charge current for capacitor 84 isquite low and the charge is completed before contact 77 closes within awelding cycle.

The trigger circuit 90 for the arc igniting circuit 80 includes atransformer 91 which is of the fiyback type and has a saturable core, ahigh voltage, secondary winding 92 and a low voltage primary winding 93of fewer turns than the secondary winding. The secondary winding 92 isconnected between electrode 850 and ground, so that electrode 85c is atground potential as rebounding of contact 52 has no effect on theconlong as no voltage is induced in winding 92. A capacitor 94 isconnected to ground and to one of the low d-c voltage supply lines, forexample, previously mentioned line 64b and through a high ohmic resistor96. The capacitor 94 serves as a temporary power supply for the triggercircuit.

One end of the primary winding 93 is connected to the junction betweencapacitor 94 and resistor 96, the other end of the primary winding 93 isconnected to one main electrode (here the cathode) of a siliconcontrolled rectifier 95 having its anode electrode grounded. The controlelectrode of rectifier 95 is connected through an RC circuit 99 to oneside of the previously mentioned switch 52, which when closed, connectsthe control electrode of the silicon rectifier 95 to the same source forthe anode potential thereof which is ground.

To explain the function of the trigger and are ignition circuits,reference is made first to FIG. 1 and to the cam configuration shown inFIG. 3. It will be recalled that at the time t the switch 52 was causedto close and that thereafter the gap between the two workpieces closes.

Switch 52 closes the control circuit for the silicon controlledrectifier or semiconductor type thyratron 95. The contact of switch 52can be expected to tinued state of conduction of semiconductor device 95As silicon controlled rectifier 95 conducts, it connects the chargedcapacitor 94 across the primary winding 93. The capacitor dischargesvery rapidly and a high voltage surge is produced across the winding 92.The peak value may be 800 volts or thereabouts. The polarity of thevoltage is immaterial but in this instance the voltage across thesecondary 92 is positive relative to ground. As stated, the electrode850 has normally ground potential but its potential is now raised byseveral hundred volts, for example, up to 800 volts. The gap 86b betweenthe electrodes b and 85c is sufficient to prevent an are at the voltageof 800 volts which prevails across the gap as long as the electrode 850is at ground potential. With the potential of electrode 850 now raisedup to about 800 volts positive, the voltage across the gap 86b increasesto about 1600 volts. Actually, before that value is reached the gapbreaks down and an arc is developed in between the two electrodes 85band 85c, immediately lowering the potential of electrode 850 toapproximately the 800 volt level of electrode 85b so that the full 1600volts becomes immediately effective across the gap 86c between theelectrodes 85a and 850 which breaks down likewise.

The delay in between the sequential or cascaded firing of the gaps 86band 86c covers a period which is in the microsecond range and below, soare the delay between firing of semi-conductor device and thedevelopment of the ignition voltage across secondary 92, so that anelectric connection is established between the electrodes 85a and 85b afew microseconds or less after the switch 52 has closed. The arcs in theelectrode system are sustained by discharge of capacitor 84. Primarywinding 83 and capacitors 84 and 87 form a high Q resonant circuit. Thehigh transformer ratio of transformer 81 causes an oscillatory voltagepulse to develop across the winding 82 with peak values in theneighborhood of 10 to 20 thousand volts, depending on the step-upratioof transformer 81.

It will be recalled that switch 51 cause, through relay 75, contact 77to close at time t.,, i.e., prior to the time t when switch 52 closes.Thus, as the high voltage peak is developed across winding 82, a voltageacross the workpieces 10 and 11 has already been established. Thisvoltage is the capacitor bank voltage in line 71, which, by itself, isinsufficient to strike an arc across the gap defined between theworkpieces, up to time At the time the voltage developed across thesecondary winding 82 raises the potential of the workpiece 11 to such anextent that breakthrough occurs with certainty instantly and onlymicroseconds or less after the initial closing of the switch 52. Thatdelay is a fixed one and does not depend upon any particular conditionssuch as the shape, size, weight, of the workpieces. As it is a fixeddelay time, with variations being of the order of electron statistics,one can regard it as a predetermined system constant. Variations inaccordance with electron statistics can be disregarded for y to sustainand continue the arc. The voltage level of bank 70 and the total amountof energy stored therein are adjusted that at the time t 'the energystored has been substantially discharged and thus converted into thermalenergy by the arc. The thermal energy has thus heated and softened theworkpiece ends for the particular period of time, 1 At the time t,, theworkpieces 10 and 11 make mutual contact and the upward motion of theworkpiece 10 continues to crowd the two workpieces together until theweld is completed.

Referring again to the arc ignition and continuation, the gaps 86b and860 break down sequentially, thereby effectively interconnectingelectrodes 85a and 85b. These two arcs initiate in the left handportions of either electrodes 85a and 85b, which is somewhat remote fromcapacitor 84, i.e., from the source which actually feeds the two arcs.These two arcs now migrate to the right to reduce the effectiveresistance in the discharge circuit for capacitor 84, and soon the arcsmerge to cross directly the gap between electrodes 85a and 85b.Electrode 85cbecomes effectively disconnected from electrodes 85a and85b so that the trigger circuit 90 is removed as a load from thedischarge circuit of capacitor 84. The removal improves the Q of thetank circuit.

As soon as an arc is ignited across workpieces l0 and 11 the effectiveimpedance across winding 82 drops to a very low value, basically that ofthe ionized gap between the workpieces, so that capacitor 84 dischargesalso into the main gap. The effective impedance of this additionaldischarge circuit is reduced in accordance with the ratio of the primaryand secondary windings of transformer 81. The energy stored in capacitor84 will rather quickly be exhausted and the arc in the electrode system85 will extinguish. The resulting open circuit state for the tankcircuit prevents any of the energy stored in capacitor bank 70 fromflowing into a parasitic circ'uit such as the now active ignitioncircuit. This, however, is not too important an aspect, as the core oftransformer 81 will saturate when the capacitor bank 70 discharges,which effectively disco'uples the ignition circuit from the maindischarge path to the two workpieces.

A complete operating cycle can be briefly described in summary asfollows. Normally the cam 40 is at rest and contacts 51 and 52 are open.Thus, relay 75 is deenergized, contact 76 is closed; the capacitor bank70 is being charged but contact 77 is open so that no potentialdifference is set up between the two workpieces. The capacitor 84 ischarged to l600 volts, but no arc exists in the electrode system 85.Capacitor 94 is charged to a low voltage. Semiconductor 95 isnonconductive.

After the workpieces 10 and l l have been positioned properly but notnecessarily very accurately, (for example, manually), switch 50 isclosed and cam 40 begins to rotate. As the workholder movesupwardworkpiece 10 contacts workpiece 11 and pushes it in upward direction. Ascontact 77 is open, no current flows between the two workpieces. Theupward motion After this prepositioning of the workpieces, switch 51closes to energize relay to disconnect the supply 63 circuit from thecapacitor bank 70 and to connect the capacitor bank to the twoworkpieces.

Switch 51 should close sufiicie'ntly ahead of the ignition of an arc tomake sure that contact 77 has ceased to rebound by the time switch 52closes. On the other hand, switch 51 should close as late as possible tokeep workpieces 10 and 11 at the same potential as long as possible as aprotective measure for personnel.

Switch 52 closes at the time t, and the first closing impact of themovable contact on the stationary contact of the switch fires thesilicon controlled rectifier 95 to produce a high voltage pulse acrosssecondary winding 92 which, in turn, fires in sequence the two gaps 86band 86c in the electrode system to thereby close the tank circuit whichincludes the two capacitors 84 and 87 and the winding 83. The resultingoscillatory discharge of capacitor 84 produces an extremely high voltagepulse across the winding 82 and an arc is struck across the gap betweenworkpieces 10 and 11. The impedance of the now ionized air gap isreduced permitting the capacitor bank 70 to discharge into theworkpieces.

At time t substantially all energy of the capacitor bank 70 has beendischarged so that by the time of contact between the workpieces 10 and11 a particular amount of thermal energy has been developed to melt themetal of the tips of the two workpieces. As the workpiece 10 is crowdedupward against the wire 11, fusion occurs and the wire 11 is retracted.The two joined pieces 10 and 11 are left in the highest position. Aftersufficient cooling, cam 40 and spring 37 cooperate to retract the joinedpieces 10 and 11. Subsequently cam 40 reaches its initial position andstops. The welded pieces can now be removed from the workholder 20.

Several outstanding features of this welding apparatus shouldbe-mentioned. For example, the gap or the particular location of the gapis not predetermined upon initially placing the workpieces into theirrespective holders. The workpiece 10, therefore, may have any kind ofsurface configuration and no accurate positioning tool for placing theworkpieces into the respective holders is required, nor does manualplacement require any great accuracy. Instead, the particular spot ofthe workpiece to which subsequently the other workpiece is to be weldedis used as a pushing surface to place the workpiece 11 into a particularposition. Thus, the entire arrangement automatically accommodates itselfto the particular configuration of the workpieces to be welded together.The points or surface areas of the two workpieces which are to be weldedtogether, are precisely the ones which are initially used to positionthe workpiece 11. Consequently, as the workpiece 10 is retracted fromthat particular position for a precise distance, the gap is definedtherewith. The initial positions of the two workpieces relative to thetwo workholders are not factors in the determination of the width of thegap.

To provide a desirable range of control over the duration of the are, achoke coil 97 is placed in parallel with a switch 98 between thesecondary winding 82 and the workholder for the workpiece l1. Normallythe switch 98 is closed to shunt the choke coil but the switch may beopened when prolongation of the duration of the arc is required. Thechoke coil 97 has a plurality of taps 97a which may be connectedselectively to the winding 82 for selected degrees of extension of theduration of the arc.

In FIG. there is shown another embodiment of the present invention. Theworkpiece and 11 are mounted in a hand gun, shown only schematically.One workpiece, here the grounded element 10 is stationary in the gun,while the other element 11 is mounted on a movable holder. A hammer 101is normally retracted at a position arrested by a releasable stop 102. Aspring 103 urges the hammer towards the holder for element 11 but isprevented by the stop 102.

The hammer 101 is electrically connected to one side of the primarywinding 93 of transformer 91; the other side of the winding 93 connectsto ground through an RC circuit 104. Secondary 92 of trans.- former 91is connected between ground and the previously mentioned electrode 850(not shown) in the electrode system 85 as in FIG. 4. The high voltagesource 65 for this embodiment may have only one output line 67. Itshould be noted, however, that the arc ignition circuit may be the sameas the one shown in FIG. 4, while the one presently described isapplicable for the welder described above with reference to FIGS. 1 to4.

- The high voltage of source 65' is applied through a filter 104 and theprimary 83 to capacitor 84. The junction between filter 104 and primary83 leads to'electrode 85b, while the other side of capacitor 84 isgrounded and also connected to electrode 85a. The remainder of thecircuit is as was described with reference to FIG. 4.

For operation switch 51 is closed first so that relay 75 can function asheretofore described and this may be done at any time before the weldinggun is triggered. Thus. the potential of the capacitor bank is appliedto workpiece II, but is insufficient to strike an arc. The stop 102 maybe released concurrently or later and spring 103 causes the hammer 101to strike towards the workpiece 11.

The hammer 101 serves as a switch for connecting electrically theworkpiece 11 to the primary winding 93 of the trigger circuittransformer 91. A small portion of the charge of capacitor 70 flows intothe RC circuit 104 and that current flows through primary 93. Thus, inthis case the electrodes 85 are fired in a similar manner except thatthe voltages are somewhat differently rated. The full 1600 volts arenormally across gap 86b and must thus not suffice to create an arc.However, the ignition voltage does not have to be large in this case tobreak that gap down. On the other hand gap 86c must break down when 1600volts are applied between the electrodes 85a and 850. Thus, theelectrode 85c must be somewhat closer to electrode 85a than toelectrode85b.

As hammer 101 contacts workpiece 11 the potential of electrode 850 israised to a level so that gap 86b between electrodes 85c and 85b breaksdown thereby causing the voltage of electrode 850 immediately to rise toa level so that gap 860 between the electrodes 85a and 85b breaks downalso. The ionized auxiliary discharge device 85 connects the capacitor84 directly across primary winding 83 and the resulting tank circuitresonates. Thus, the main arc ignites across the gap between workpiecesl0 and 11 as aforedescribed. Turning now to a second function of thehammer 101, its motion is predetermined by the characteristics and biasof spring 103. Thus, hammer'10l pushes the workpiece 11 towards theworkpiece 10. at a controlled rate to complete the weld. This deviceworks satisfactorily in case the weight and size of the workpieces arerather constant; otherwise, weight variation of the particular workpiecethat is being moved may cause variation in the time between the arcignition and the contact making. No such variation occurs in the deviceshown and explained with reference to FIGS. 1 through 4.

FIG. 7 is a visual summary of the stages of relative movement betweenthe two workpieces 10 and 11 at the different times t In FIG. 7 it isassumed that I occurs on the cam slope 415 just before t FIG. 7e showsthe relative positions of the two workpieces at and FIG. 7f shows an aredesignated 300 that is established at that instant. FIG. 7 further showshow the two workpieces make mutual contact at 2 and are then crowdedtogether to make the finished weld that is accomplished at t,.

FIG. 7 makes clear that with the two workpieces l0 and 11 positioned atrandom in the corresponding workholders in such manner that the twoworkpieces abut each other at t the starting gap that is provided inpreparation for the welding operation is determined solely by theretraction of the movable workholder from the position 1 so that the gapat t is an accurately predetermined gap that will be formedautomatically on each operating cycle. At t, the two workpieces arecharged with a voltage as indicated and the arc may be established atthe gap dimension shown in 1 which is the starting gap because t and t,are spaced apart by a cam dwell of constant radius; or the establishmentof the arc may be delayed until the two workpieces are relatively closetogether as indicatedat FIG. 7f.

Referring back to FIG. 3 it may be seen that the dwell 414 is ofsubstantial circumferential extent and the leading slope 415 of thesecond lobe is of substantial circumferential extent. It is apparenttherefore that there is a substantial range for adjustment of theduration of the arc. For example, the range of adjustment may be from300 microseconds to 3 milliseconds.

FIGS. 8 and 9 show how two workholders 20a and 22a corresponding to thepreviously mentioned workholders 20 and 22 may be adapted for a fullyautomatic cycle which includes automatic clamping of the two workpieces10 and 11. The workholder 20a is in the form of a rod,one end of whichconstitutes a cam follower 36a that corresponds to the previouslydescribed cam follower 36 and cooperates in the same mannerwith thepreviously described cam 40.

The workholder 20a has a noncircular shank portion 200 which isslidingly mounted in a pair of spaced guides 202 and 204 with a coilspring 205 under compression between the guide 204 and a collar 206 onthe workholder to bias the follower 36a effectively against the cam 40.The workholder 20a has a leading stem portion 208 which forms a seat toreceive the workpiece 10, the stem portion being removable to permit thesubstitution of a different stem portion to accommodate a workpiece ofdifferent shape or dimension. A pair of jaws 210 is mounted on pivots212 to releasably clamp the workpiece 10 and the two jaws havecorresponding operating arms which are connected by a pair of togglelinks 214 to a pivot 215 on an armature 216 of a clamping solenoid 218.The armature 216 is normally advanced with the two jaws 210 open asshown in FIG. 8 but energization of the solenoid 218 retracts thearmature to close the jaws 210 to tightly grip the workpiece.

, The stationary workholder 22a is formed with a straight groove 220 toslidingly seat the wire or workpiece 11 and a jaw 222 is provided toclamp the workpiece in the groove. The jaw 222 is mounted on a pivot 224and has an operating arm 225 that is connected by a coil tension spring226 to the armature 228 of a clamping solenoid 230. Here again thearmature 228 is normally extended with the jaw 222 retracted andenergization of the solenoid 230 retracts the armature to close the jaw.The spring 226 has a relatively light spring force which is sufficientto cause the workpiece 11 to be retained in the required slidablemanner.

Preferably the workholder 20a is further suitably provided with anejection solenoid 232 having anormally retracted armature 234. When thesolenoid 232 is energized the armature 234 advances with a snap actionto eject the finished welded product at the end of the operating cycle.

FIG. 6 indicates diagrammatically how a cam assembly of five rotary camsmay be mounted on a common cam shaft (not shown) to carry out a fullyautomatic cycle which includes the steps of temporarily clamping the twoworkpieces and subsequently ejecting the finished welded product. Thefive cams comprise: the previously mentioned cam 40 which cooperateswith the follower 36a to control the movable workholder 20a in themanner heretofore described; a cam 240 having a circumferentiallyextensive upper dwell 241 to cooperate with a normallyopen switch 242for energizing the two clamping solenoids 218 and 230 throughout themajor portion of the operating cycle; a cam 244 having a lobe with anupper dwell 245 to operate an associated switch 510 which corresponds tothe previously mentioned switch 51 for placing a voltage across the twoworkpieces; a cam 246 carrying a contact 247 to cooperate with a contact248 to serve as an arc-triggering switch in the manner of the previouslymentioned switch 52; a cam 249 having a short lobe 250,to operate acooperative switch 251 for momentarily energizing the ejection solenoid232; and finally, a cam 252 having a short lobe 253 to open a normallyclosed switch 254 to terminate the rotation of the cam assembly.

As shown in FIG. the normally stationary contact 248 may be mounted onan arcuate rack 260 that is concentric tothe cam shaft and is rotatablysupported thereon by a pair of arms 262. Teeth 264 of the arcuate rackmesh with a worm 265 on an adjustment shaft 266 that is manuallyoperable by a knob 268. The knob 268 carries a pointer 270 which, asindicated in FIG. 11, is movable along a graduated scale 272 that iscalibrated in terms of microseconds of arc duration. For example, thescale 272 may show a range from 6 millisecond to 8 milliseconds.

FIG. 12 indicates how the previously described circuit in FIG. 4 may bemodified for cooperation with the cam arrangement shown in FIG. 6. Theswitch 50 is a push button switch which energizes a relay having a earnnormally open locking contact 274 in a locking circuit that includes thepreviously mentioned switch 254 that is normally closed and is openedwhen released by the cam lobe 253. Thus momentarily depressing thestarter switch long enough to permit switch 254 to close causes onerotation of the cam shaft to be carried out automatically. First the twoclamping solenoids 214 and 230 are energized and subsequently the switch51a is operated by the cam 245 to set up the required voltage across thetwo workpieces. Still later the cam con-- tact 247 of FIG. 6 cooperateswith contact 248 to initiate the welding arc. After the heated workparts abut with each other the switch 51a is released by the cam lobe245 for recharging the capacitor bank and subsequently the energizationof the two clamping solenoids by the switch 242 is terminated. Then thecam lobe 250 closes the switch 251 momentarily to operate the ejectionsolenoid 232 to eject the welded product. Finally, cam lobe 253 opensthe switch 254 to break the relay locking circuit to operate the clutch45b and the brake 45a to stop the cam assembly.

In a typical embodiment of the invention, the motor 47'operates at 1800rpm and incorporates reduction gearing which steps down the velocity byone sixth to rotate the shaft 46 at approximately 300 rpm. When theclutch 45b is closed an auxiliary mass is added to the constantlyrotating structure, which auxiliary mass includes parts of the clutch45b, parts of the brake 45a, the shaft 44, the gears 42 and 43 and therotary cam means along with the shaft on which the rotary cam means ismounted. With the major portion of the driving mass constantly rotatingat 1800 rpm and a minor portion thereof constantly operating at 300 rpmand with the auxiliary mass that is added by the clutch 45b andassociated parts quickly accelerated to 300 rpm to start an operatingcycle and with all of these rotating parts having a combined weight ofapproximately 2% pounds the momentum available for actuating the movableworkholder 20a is exceedingly high relative to the inertia of the sixounce workholder 20a. It may be readily appreciated that the drivingmomentum is so overpowering that the effect of picking up the auxiliaryweight including the cam means is insignificant and full acceleration ofthe cam means is accomplished in advance of the operating cycle, i.e.before the cam 40 starts to actuate the workholder 20a.

Whenever a change over to the welding of different workpieces requires achange in the rate at which the gap between the two workpieces isclosed, it is a simple matter to substitute a new cam 40 having lobeswith slopes of different inclination.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be covered by thefollowing claims.

We claim:

1. In an apparatus for joining two workpieces by arc welding, thecombination of:

two workholders for the two workpieces, respectively, normally spacedapart to provide a gap between the two workpieces;

cam means;

follower means cooperative with the cam means and operatively connectedwith at least one of the two workholders to cause relative movementbetween the two workholders to close the gap between the two workpieces;

a power actuated structure normally-rotating in a steady state conditionwith relatively high momentum;

means tooperatively connect the rotating structure with the cam meansfor actuation thereof through one operatingcycle which includes closingthe gap between the two workpieces;

means responsive to thecam means to place a voltage across the twoworkpieces during the operating cycle before the gap closes; and

means responsive to the cam means to strike an arc between the twoworkpieces while said voltage exists and before the gap closes.

2. A combination as set forth in claim 1 which includes means on the twoworkholders respectively responsive to the cam means to releasably gripthe two workpieces early in the operating cycle and subsequently torelease the two workpieces.

3. A combination as set forth in claim 1 which includes means responsiveto the cam means to eject the welded product at the end of the operatingcycle.

4. A combination as set forth in claim 1 which includes:

capacitor means;

means responsive to the cam means to place a charge on the capacitormeans; and

means responsive to the cam means to connect the two workpieces to thecapacitor means thereby to place said voltage across the two workpieces.

5. A combination as set forth in claim 1 inwhich said means to strike anarc is manually adjustable relative to the cam means to vary the pointin the operating cycle at which the arc is created.

6. A combination as set forth in claim 5 which includes indicator meansresponsive to adjustment of the means to strike the are.

7. A combination as set forth in claim 6 in which said indicator meansis calibrated in terms of units of time measuring the interval betweenthe striking of the arc and the closing of the gap between the twoworkpieces.

8. A combination as set forth in claim 1 which includes means on one ofsaid workpieces to yieldingly retain the corresponding workpiece in amanner to permit forcible sliding retraction of the correspondingworkpiece by the other of the two workpieces.

9. A combination as set forth in claim 8'in which said cam means is of acontour to cooperate with said follower means to close the gap betweenthe two workpieces two times in succession in the working cycle topermit said one workpiece to be retracted the first time for the purposeof establishing a predetermined gap between the two workpieces beforethe arc is created.

10. A combination as set forth in claim 8 in which said cam means is ofa contour to continue to urge the two workpieces together after the gapis closed and while the two workpieces are heated by the are, thereby tocrowd the two workpieces together for mutual'fusion,

whereby the force with which the two workpieces are crowded together islimited by the degree of resistance to retraction of the yieldinglyretained workpiece.

11. A combination as set forth in claim 1 in which the means tooperatively connect the power actuated structure to the cam meansincludes speed reducing means.

12. In an apparatus for joining together pairs of workpieces by arcwelding in repeated operating cycles, the combination of:

rotary cam means;

two workholders to hold the two workpieces in positions with apredetermined starting gap between the two workpieces;

follower means cooperative with the cam means to cause relative movementbetween the two workpieces to close the gap between the two workpieces;I

means controlled by said cam means to replace a voltage across the twoworkpieces prior to the closing of the gap;

means controlled by the cam means to apply a high frequency pulse acrossthe two workpieces thereby to trigger an arc prior to the closing of thegap;

a driving mass;

means to rotate the driving mass at a substantially constant velocity;and means to operatively connect the cam means to the driving mass forone cycle of operation of the cam means, I

whereby the flywheel effect of the rotating driving mass causes thesuccessive cycles to be precisely identical with respect to theirpatterns of movement of the timing relationships involved.

13. A pulse arc welder comprising:

workpiece holding means constructed for providing reciprocating motionto move a pair of workpieces towards each other and away from eachother, the pair of workpieces moving in unison relative to the holdingmeans when the work pieces contact each other during a continued motionof the holding means for moving the workpieces towards each other, theposition of either of the pair of workpieces relative to the holdingmeans being maintained when the work pieces are moved subsequently awayfrom each other by the holding means;

motion control means for the holding means for controlling the moving ofthe workpieces into contact for positioning the workpieces relative tothe holding means, for moving the workpieces away from each other andfor subsequently moving the workpieces towards each other again at acontrolled rate from a predetermined distance into contacting position;

first control means for applying to the workpieces a voltage when thedistance of the workpieces from each other is insufficient to causestriking of an are, but sufficient to sustain an existing arc; and

second control means operatively coupled to the motank circuit.

15. A pulse arc welder as set forth in claim 13 wherein the circuitmeans include variable impedance means through which the high voltagepulse is applied to the gap.

1. In an apparatus for joining two workpieces by arc welding, thecombination of: two workholders for the two workpieces, respectively,normally spaced apart to provide a gap between the two workpieces; cammeans; follower means cooperative with the cam means and operativelyconnected with at least one of the two workholders to cause relativemovement between the two workholders to close the gap between the twoworkpieces; a power actuated structure normally rotating in a steadystate condition with relatively high momentum; means to operativelyconnect the rotating structure with the cam means for actuation thereofthrough one operating cycle which includes closing the gap between thetwo workpieces; means responsive to the cam means to place a voltageacross the two workpieces during the operating cycle before the gapcloses; and means responsive to the cam means to strike an arc betweenthe two workpieces while said voltage exists and before the gap closes.2. A combination as set forth in claim 1 which includes means on the twoworkholders respectively responsive to the cam means to releasably gripthe two workpieces early in the operating cycle and subsequently torelease the two workpieces.
 3. A combination as set forth in claim 1which includes means responsive to the cam means to eject the weldedproduct at the end of the operating cycle.
 4. A combination as set forthin claim 1 which includes: capacitor means; means responsive to the cammeans to place a charge on the capacitor means; and means responsive tothe cam means to connect the two workpieces to the capacitor meansthereby to place said voltage across the two workpieces.
 5. Acombination as set forth in claim 1 in which said means to strike an arcis manually adjustable relative to the cam means to vary the point inthe operating cycle at which the arc is created.
 6. A combination as setforth in claim 5 which includes indicator means responsive to adjustmentof the means to strike the arc.
 7. A combination as set forth in claim 6in which said indicator means is calibrated in terms of units of timemeasuring the interval between the striking of the arc and the closingof the gap between the two workpieces.
 8. A combination as set forth inclaim 1 which includes means on one of said workpieces to yieldinglyretain the corresponding workpiece in a manner to permit forciblesliding retraction of the corresponding workpiece by the other of thetwo workpieces.
 9. A combination as set forth in claim 8 in which saidcam means is of a contour to cooperate with said follower means to clOsethe gap between the two workpieces two times in succession in theworking cycle to permit said one workpiece to be retracted the firsttime for the purpose of establishing a predetermined gap between the twoworkpieces before the arc is created.
 10. A combination as set forth inclaim 8 in which said cam means is of a contour to continue to urge thetwo workpieces together after the gap is closed and while the twoworkpieces are heated by the arc, thereby to crowd the two workpiecestogether for mutual fusion, whereby the force with which the twoworkpieces are crowded together is limited by the degree of resistanceto retraction of the yieldingly retained workpiece.
 11. A combination asset forth in claim 1 in which the means to operatively connect the poweractuated structure to the cam means includes speed reducing means. 12.In an apparatus for joining together pairs of workpieces by arc weldingin repeated operating cycles, the combination of: rotary cam means; twoworkholders to hold the two workpieces in positions with a predeterminedstarting gap between the two workpieces; follower means cooperative withthe cam means to cause relative movement between the two workpieces toclose the gap between the two workpieces; means controlled by said cammeans to replace a voltage across the two workpieces prior to theclosing of the gap; means controlled by the cam means to apply a highfrequency pulse across the two workpieces thereby to trigger an arcprior to the closing of the gap; a driving mass; means to rotate thedriving mass at a substantially constant velocity; and means tooperatively connect the cam means to the driving mass for one cycle ofoperation of the cam means, whereby the flywheel effect of the rotatingdriving mass causes the successive cycles to be precisely identical withrespect to their patterns of movement of the timing relationshipsinvolved.
 13. A pulse arc welder comprising: workpiece holding meansconstructed for providing reciprocating motion to move a pair ofworkpieces towards each other and away from each other, the pair ofworkpieces moving in unison relative to the holding means when the workpieces contact each other during a continued motion of the holding meansfor moving the workpieces towards each other, the position of either ofthe pair of workpieces relative to the holding means being maintainedwhen the work pieces are moved subsequently away from each other by theholding means; motion control means for the holding means forcontrolling the moving of the workpieces into contact for positioningthe workpieces relative to the holding means, for moving the workpiecesaway from each other and for subsequently moving the workpieces towardseach other again at a controlled rate from a predetermined distance intocontacting position; first control means for applying to the workpiecesa voltage when the distance of the workpieces from each other isinsufficient to cause striking of an arc, but sufficient to sustain anexisting arc; and second control means operatively coupled to the motioncontrol means for applying a high voltage across the workpieces at theinstant when the workpieces move from a particular distance towards eachother at the controlled rate.
 14. A pulse arc welder as set forth inclaim 13 in which the second control means includes a high frequencytank circuit and an auxiliary discharge gap in the tank circuit furtherincluding a control circuit for controlling the ionization of theauxiliary discharge gap, the control circuit being under control of themotion control means for ionizing the discharge gap causing the tankcircuit to resonate, and circuit means for connecting the tank circuitto the workpieces to ignite an arc across the workpieces upon theresonance of the tank circuit.
 15. A pulse arc welder as set forth inclaim 13 wherein the circuit means include variable impedance meansthrough which the high voltage puLse is applied to the gap.